This invention relates to a rotary power device, preferably for tensioning mechanisms of safety devices, in particular safety belts, for the protection of passengers in conveyances. Such a device includes a housing, a compressed-gas generator associated with the housing, and a compressed-gas-actuated drive element guided in the housing for a shaft to be rotated.
U.S. Pat. No. 3,845,836 to Bendler et al discloses a safety belt for the protection of the passengers of conveyances, e.g. airplanes or automotive vehicles, provided with a tensioning mechanism. This tensioning mechanism is triggered in an accident situation by means of a sensor upon exceeding a predetermined deceleration value and retracts and/or reels in the belt until the latter is in sufficiently close contact with the body of the passenger. Such a sensor has been described, for example, in German published unexamined application DOS 2,207,831. The tensioning mechanism, fashioned as a rotary power apparatus or element, has a housing with a compressed-gas generator arranged therein and with a shaft connected with the end of the belt to be retracted. The drive element for the shaft is a turbine wheel operated by means of compressed gas. To avoid injury to the passenger during the tensioning step, the tensioning mechanism cooperates with belt force limiters, such as a torsion bar or a friction (friction wheel) brake. Furthermore, a blocking device which becomes automatically effective is provided which arrests the belt at least for short-term stresses. For this purpose, a serrated ratchet wheel with a spring-loaded pawl can be used, for example.
A considerable increase in the protective effect of safety belts is attained by means of such tensioning devices if these belts -- as is often the case under practical conditions -- are applied relatively loosely by the passenger to avoid excessive restriction of his freedom of movement.
The protective effect is also improved by such tensioning mechanisms in conjunction with the so-called automatic belts which yield during slow movements but block during rapid motions and which, due to a restoring spring, always contact the passenger's body with slight tensile stress. This is so, because on the one hand the blocking systems of the automatic belts, which can be triggered by inertial forces, operate at a certain delay and on the other hand, the belt section wound on the shaft is applied thereto with a certain amount of looseness, rather than being reeled completely tightly thereon. Further, the belt itself is stretchable, and the seat, the clothing, as well as the upper part of the passenger's body are additionally compressed under the pressure action of the safety belt, so that in an accident situation an undersirably extensive forward movement of the passenger's body is still possible. By a retraction of the belt with the aid of such tensioning mechanisms, such undersirable forward movement can advantageously be avoided.
The number of revolutions to be executed by the shaft of the tensioning mechanism during the tensioning process depends on the retraction path required in an individual case, on the reel diameter, etc. In general, more than one revolution of the shaft is required, which is readily possible by means of the turbine wheel referred to above with its plurality of exposure surfaces arranged distributed along the periphery. However, a prerequisite for operation of the turbine wheel is a correspondingly long-term effect of the compressed gas on the individual exposure surfaces of the turbine wheel moving in succession past the compressed-gas generator whereby, in total, an often undesirable prolongation of the tensioning procedure occurs.
This invention contemplates apparatus which avoids the disadvantages in a rotary power element or device of the type mentioned hereinabove. That is, this invention contemplates a rotary power device such that, with a minimum of manufacturing expenses and with high reliability, this device makes it possible to execute more than one revolution of the shaft within a minimally short time period and at maximally low gas pressures.
The present invention provides that the drive element is constructed as a rotary piston with a piston surface which can be under the effect of the compressed gases, this piston being connected or connectible, via an annular-cylindrical piston foot (base), with the shaft in the peripheral direction by positive coupling and being displaceable axially with respect to this shaft. The rotary piston of the device of the present invention is furthermore guided in a helically wound duct of the housing arranged coaxially to the shaft, the lateral boundary walls of the duct extending to the piston foot. By means of constructing the drive element as an axially shiftable rotary piston with a single piston surface to be exposed to the compressed gases, it is advantageously possible, as contrasted to the turbine wheel, to immediately make the full gas pressure effective on the piston area so that the rotary piston has imparted thereto a high initial velocity and accordingly exerts advantageously a high torque on the shaft to be rotated. As the compressed-gas generator for the production of the compressed gases, it is possible, for example, to use a compressed-air bottle which is under a correspondingly high internal pressure. With a view toward minimum amount of space to be occupied by the device, however, a propellant charge element is preferably provided for the compressed-gas generator, ignitable electrically or mechanically by percussion and producting the compressed gases only during its reaction. The propellant charge element can be composed, for example, in accordance with the mixtures indicated in German Patent 1,646,313.
The connection between the rotary piston and the shaft is to be such that, on the one hand, the torque can be flawlessly transmitted from the rotary piston to the shaft and, on the other hand, the rotary piston is displaceable axially relative to the shaft with minimum forces. For this purpose, the shaft and the annular-cylindrical piston foot of the rotary piston can be fashioned, for example, in the manner of a multiple-groove (multiple-slot) profile. To render the manufacturing process maximally simple, however, the shaft and the piston foot are instead preferably provided with at least respectively one axial groove and a slide spring inserted therein, the latter establishing the positive connection in the peripheral direction but permitting in the axial direction the displacement between the shaft and the rotary piston.
The guide duct which is helically formed within the interior of the housing represents, so to speak, the cylinder for the rotary piston. The length of this duct is dependent on the number of revolutions to be executed by the rotary piston and/or by the shaft; this number of revolutions depends, for example, with the use of the rotary power element for tensioning mechanisms of safety devices, particularly safety belts, on the required retraction distance of the end of the safety device connected to the shaft to be rotated. The steepness or pitch of this duct is maintained, with a view toward a maximally short axial structural length of the housing, to be so small as permitted by the axial width of the rotary piston and by the thickness of the boundary walls required for reasons of strength. The boundary walls extend to the annular-cylindrical piston foot to prevent the compressed gases from flowing laterally around the rotary piston and escaping into the section of the guide duct disposed still in front of the rotary piston, since these compressed gases are not only lost for the advancement of the rotary piston, but would even brake the movement of the latter. To keep the friction losses at a minimum, it is advantageous to keep the play relatively large between the surfaces moving relatively to each other, except for a preferably narrow, strip-shaped zone on the two sides of the rotary piston and on the skirt surface thereof.
With the aforementioned connection possibilities between the rotary piston and the shaft, the two parts are initially positively coupled in the peripheral direction. Thus, the shaft cannot be freely rotated with respect to the rotary piston, for example, also during the normal operating condition of the automotive vehicle, i.e. prior to the beginning of the tensioning process. This embodiment of the rotary power element, therefore, is suitable, for example, for simple safety belts, the length of which does not automatically adapt itself to the respective situation but must rather be adjusted manually. However, in contrast to the embodiment discussed immediately above, in case of so-called automatic belts, the shaft, in the normal operating condition, must be freely rotatable with the one end of the safety belt wound thereon, since only in this case can the safety belt be unreeled off the shaft, for example when the passenger bends forward, and can again be wound up when the passenger leans back, by means of a restoring spring which sets the shaft into rotation.
In order to be able to employ the rotary power element or device of this invention even if the shaft to be rotated must be freely turnable up to the beginning of the drive process, for example in the tensioning procedure of an automatic belt, a further advantageous embodiment of the invention provides that a driving bush is arranged between the shaft and the piston foot, with respect to which the shaft is freely rotatable until the beginning of the drive process. At the beginning of the drive process, both the bush and the shaft are then positively lockable together in the peripheral direction in the axial advancing direction of the rotary piston, under displacement of the driving bush. Furthermore, the rotary piston is positively connected with the driving bush in the peripheral direction and is displaceable on the bush in the axial direction. The connection between the rotary piston and the driving bush is preferably effected by means of groove and spring -- as indicated above for the direct connection of rotary piston and shaft. If, at the beginning of the drive process, the rotary piston is set into rotation under the effect of the compressed gas and is simultaneously advanced in the axial direction by the forced guidance in the helically wound guide duct, then the rotary piston entrains the driving bush due to friction thereagainst, i.e the piston shifts the bush forward in the axial direction until the bush is positively joined to the shaft in the peripheral direction so that the piston torque is transmitted to the shaft.
The positive connection in the peripheral direction between the driving bush and the shaft can be effected, for example, by means of a radial pin inserted in the shaft, which pin engages, after a corresponding rotation and axial displacement of the driving bush, in an axial slot of the latter. To be able to establish the positive connection between the driving bush and the shaft with maximum speed after the beginning of the drive process by the rotary piston, i.e. to transfer the rotary movement of the piston maximally early to the shaft, another suggestion of the invention provides instead that the driving bush has a serration on its annular end face located at the front -- as seen in the axial advancing direction of the rotary piston -- this serration, together with a corresponding serration on an opposite end face of the shaft establishing the locking action. The depth and width of the teeth are suitably chosen to be just as large as required for reasons of strength for the safe transmission of the torque, so that a minimum of axial displacement and optionally rotation of the driving bush are sufficient to get the two serrations to mesh with each other and thus to effect the locking in the peripheral direction.
According to a further suggestion of this invention, the opposite end face of the shaft is formed with a coupling sleeve pushed onto the shaft and firmly joined thereto. This affords the possibility of producing the coupling sleeve, just as the driving bush, of a material of a higher strength than the shaft. The coupling sleeve can be firmly joined to the shaft, for example, by means of a cross pin or by means of shrink fitting, but preferably the sleeve is firmly joined to the shaft by way of a further serration at its front end face which is in constant engagement with a corresponding serration of the shaft, so that with the same strength minimum structural sizes are obtained.
According to the invention, the further provision is made that the tooth flanks coming into contact with the counter teeth are -- as seen from the bottom of the tooth -- inclined, in case of the driving bush, to a minor extent in the rotation direction of the rotary piston and, in case of the shaft and/or the coupling sleeve, in opposition thereto. This effects advantageously an automatic reinforcement of the axial contact of the two meshing serrations.
To further shorten the time interval between the triggering of the compressed-gas generator and the mutual locking action between the driving bush and the shaft, another suggestion of this invention provides the formation of a small gas accumulation chamber behind the driving bush which is in the starting position. This gas backup chamber is connected with the pressure chamber or space between the compressed-gas generator and the rotary piston in the starting position, for example by way of an opening or bore. The compressed gases then are not only effective on the piston area of the rotary piston but also immediately on the rearward end face of the driving bush, whereby the latter is already shifted in the advancing direction of the rotary piston and is positively locked together with the shaft in the peripheral direction before the rotary piston proper has moved markedly in the axial direction and has exerted corresponding axial forces on the driving bush. This sudden effect on the driving bush and thus the locking together thereof with the shaft takes place so rapidly that the rotary motion of the rotary piston is advantageously transmitted to the shaft practically from the very beginning. The gas accumulation (backup) chamber is fashioned to be small to avoid an unnecessary expansion of the gases and an ensuing reduction in pressure.
To keep the friction during the relative movement between the driving bush and the shaft at a minimum, another suggestion of this invention provides a ball bearing between the shaft and the driving bush, wherein the balls are preferably distributed not only in a row along the circumference, but in axial succession in two or more rows, so that the forces exerted by the rotary piston on the driving bush and thus also on the shaft are transmitted over a maximally large surface area. However, in place of a ball bearing, it is also contemplated by the invention to provide a sliding bearing depending on the circumstances of each individual case, optionally together with an additional coating of an antifriction material, such as, for example, polytetrafluorethylene (= "Teflon").
The free rotatability of the shaft up to the beginning of the driving operation can, by the way, also be advantageously ensured by arranging, according to the invention, the driving bush rotatably on a trunnion coaxially disposed with respect to the shaft and firmly joined to the housing and providing that the driving bush is axially displaceable in the forward direction toward the shaft. The shaft and the trunnion are thus fashioned separately from each other, so that the mobility of the shaft is not affected by the driving bush until the driving bush has been shifted axially with respect to the shaft under the effect of the compressed gas, along the trunnion, and has been positively locked together with the shaft in the peripheral direction.
In connection with the ball or sliding bearing on the shaft, as well as in connection with the arrangement of a special trunnion for the driving bush, it is advantageous to maintain the radial play between the shaft or trunnion and the driving bush at a low level in the rearward zone of the bush, so that a minimum of compressed gas flows from the gas accumulation chamber behind the driving bush to the front end of the driving bush and perhaps also into the guide duct, and thus the displacement of the driving bush and the rotary piston is practically unimpeded thereby.
According to the invention, it is furthermore contemplated to arrange an annular sealing element in the zone of the rear end of the driving bush between the latter and the rotary piston to reduce the gas flow around the outside of the driving bush. The sealing element, fashioned for example as an O ring inserted in a corresponding annular groove, can simultaneously serve for the axial fixation of the driving bush with respect to the rotary piston until the beginning of the drive process, by forming this sealing element with a corresponding, radial overdimension, so that the driving bush and the rotary piston are frictionally joined with each other.
According to a further suggestion of the invention, the axial fixation of the driving bush up to the beginning of the drive process can be still further improved by fashioning the sealing element as an annular edge radially outwardly projecting on the driving bush and in contact with the piston foot, which edge can be sheared off. The driving bush is inserted by frictional connection with its annular shearing edge in a corresponding annular recess at the rear end of the rotary piston and thereby effects simultaneously an advantageous sealing action.
For obtaining a maximally favorable relationship between the pressure force effective on the rotary piston and the torque exerted by the latter, the piston area of the rotary piston under the exposure of the compressed gases is formed, according to the invention, as a planar surface lying in one of the axial planes of the piston. The term axial plane is understood to mean the planes extending through the longitudinal axis of the rotary piston. The longitudinal axis of the rotary piston extends coaxially to the axis of the shaft.
The length of the rotary piston, curved in correspondence with the helically wound guide duct, is to be selected so great that the pressure forces effective on the rotary piston are flawlessly transmitted to the piston foot, i.e. without destruction or undue deformation of the rotary piston. In general, an exceeding of this minimum length in the peripheral direction, required for reasons of strength, which also requires a correspondingly larger axial length of the rotary piston, should be avoided, since this requires, with an equally large angle of rotation, a correspondingly longer guide duct and thus also a housing which is longer in the axial extension. To maintain the friction between the rotary piston and the boundary walls of the guide duct at a minimum, the invention provides that the rotary piston is fashioned with an axial width and radial height which diminish in the direction of rotation. The smallest axial and radial play between the rotary piston and the boundary walls is thus limited to a small zone on the piston surface under the effect of the compressed gases. To reduce the axial width of the rotary piston, its two lateral surfaces are preferably inclined toward each other, which provides the further advantage that the rotary piston abuts with its front face the housing and/or the front end of the guide duct only after a larger angle of rotation.
To further reduce the friction, another embodiment of this invention provides that the rotary piston is equipped, close to the piston area under the effect of the compressed gases, with one or more notches or slots and with disk-shaped sealing elements inserted in such notch or notches which project outwardly to a minor extent in the axial and radial directions and are in contact with the wall of the duct formed within the housing. The notch or notches extends or extend, just as the piston area, preferably in axial planes and run practically up to the piston foot. A thin metal sheet of, for example, steel, aluminum, copper, or lead, but especially of brass, is frictionally mounted in the notch or notches. This makes it possible to increase the play between the rotary piston and the wall of the guide duct in the zones lying outside such notch or notches, as compared to a rotary piston without such notches, without thereby impairing the sealing effect with respect to the compressed gases.
To further reduce the gas leakage to the part of the guide duct in front of the rotary piston, it is contemplated according to this invention to provide the piston foot on its outer wall or skirt surface with a helically wound groove in which the boundary walls of the duct formed in the housing extend in the manner of the labyrinth seal.
The rotary piston is maintained, until the beginning of the drive (actuation) process, in the starting position with its piston area lying in opposition to the compressed gas generator. This fixation can be executed basically by inserting the rotary piston in the guide duct by friction seat (mounting), so that the piston can be shifted under the effect of the compressed gases, but cannot be displaced, for example, under the forces occurring during the normal operating condition. However, insofar as use is made of the aforementioned advantageous measures to reduce friction, such a friction mounting is unnecessary. In this case, according to a further feature of this invention, the rotary piston is held in its starting position by means of a shearing element. The shearing element is preferably fashioned as a safety pin (locking pin) disposed in an axial housing bore in a corresponding bore of the rotary piston.
For an advantageous exploitation of the energy of the compressed gases, it is furthermore recommended to arrange the compressed-gas generator and/or its outlet duct in the housing so that the compressed gases, in the starting position of the rotary piston, flow vertically against the piston area thereof, i.e. they are introduced essentially tangentially into the guide duct.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.